In recent years, there has been great emphasis placed on burglar alarm systems which set off an alarm in the event there is an unauthorized opening of doors and/or windows. In the area of window security, typical prior art installations include switching circuits which are "made" or "interrupted" in the event that the bottom window or top window of a two window installation is moved to an open position by an unauthorized person. Recent prior art systems of this type typified by U.S. Pat. Nos. 3,596,021 and 3,710,369, employ magnetically operated switches which are switched between an open and closed position in response to the movement of an associated permanent magnet carried by the slidably mounted window elements.
One of the major drawbacks of prevalent burglar alarm systems of this type is the requirement that the switchable element activated by the selective closing and opening of the window elements have to be individually installed on the window frame of each window unit which is to be protected.
Another difficulty inherent in prior art burglar alarm systems of this type is their inability to simply and inexpensively taken into account the employment of a third window element such as a screen and the desirability of the home owner opening either the lower or upper window sash when the storm window or screen is located in front of the sash being opened.